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Hi TI,
I am having trouble with troubleshooting the hardware of the TPIC1021 LIN bus interface module in an automotive environment.
My configuration for the 1 master device and 2 slave devices are as follows:
- LIN wire connected directly to the LIN pin of the TPIC1021;
- MASTER DEVICE ONLY - LIN wire pulled high via 1k resistor and series diode;
- Vsupply connected to 12V supply voltage;
- GND connected to common ground;
- INH not connected;
- NWake not connected;
- EN pin directly connected to 3.3V;
- RXD pin directly connected to MCU UART RX;
- TXD pin directly connected to MCU UART TX;
The MCU for all three devices is the STM8S103F3, which uses the normal UART protocol to for transmit and receive. Both the TX and RX are internally pulled high and communication is commenced by a logic low on the TX pin, followed by the address of the slave and the command. Communication is detected on the RX by a falling edge trigger.
The communication between the two MCUs works fine on the workbench when the two TPIC1021s (master & slave) are removed. However, when the two interface modules are included between the two MCUs, there appears to be no communication on the LIN wire. Unfortunately I don't have a scope, only a Saleae Logic analyser which is not 12V tolerant. As such, instead of dynamically testing the communication, I tried to perform static tests as follow:
- Provide power to the MCU (3.3V) and the TPIC1021 (12V);
- Initial state - EN=3.3V, RXD and TXD pulled high from MCU;
- Alternatively pulling the LIN wire and the TX of the MCU low;
The results were not quite as helpful as I had hoped. Pulling the TX low had no effect on the LIN IO pin; however pulling the LIN wire low resulted in a logic low on the RXD pin as expected. I am uncertain as how to proceed with the troubleshooting. The situation would've been mitigated if I had an oscilloscope or a 12V tolerant logic analyser, but alas, that is not possible at the time being.
My questions are:
- Does the LIN interface module initially enter low power or standby mode and waits for a wake up condition?
- There is constant 3.3V on the EN pin, so does the module wait for an explicit EN low to high for wake up after power up?
- Does the NWAKE pin being not connected affect the TPIC1021?
- Is there a specific logic condition on the TXD pin that has to be met before the LIN pin follows the TXD pin?
I have uploaded the schematic involving the LIN-MCU connections. Due to company intellectual property, I cannot upload the entire schematic.
Any help with the above will be greatly appreciated. Thank you in advance.